1. Field of the Invention
This invention relates to a process for producing at least three fractions, including a deep oil cut, from heavy hydrocarbon materials containing asphaltenes.
2. Brief Description of the Prior Art
Many methods for extracting various fractions from bituminous materials have been disclosed previously in the prior art, perhaps the most well known of these being termed "propane extraction" in which asphaltic materials are extracted or recovered from heavy hydrocarbon materials such as reduced crudes by means of a single solvent extraction step using propane as the extractant. However, it has been found that in operation, plugging of the extraction equipment frequently occurs in the section between the site of introduction of the propane and the site of introduction of the feed, thereby making continuous operation difficult.
U.S. Pat. No. 2,940,920, assigned to the same assignee as the present invention, discloses that solvents other than propane can be used to separate heavy hydrocarbon materials into at least two fractions at a greatly improved rate of separation and in a manner which eliminates certain prior art operating difficulties encountered in the use of propane type solvents (C.sub.2 to C.sub.4 hydrocarbon solvents). That patent discloses effecting the separation by using high temperature-pressure techniques and by using pentane as one of a group of suitable solvents. Such practice permits a deeper cut to be made in the heavy hydrocarbon material, but as a consequence, more resinous bodies are present in the resulting oil fraction, tending to decrease the quality of that oil.
U.S. Pat. No. 4,125,459, assigned to the same assignee as the present invention, discloses a process for separating a heavy hydrocarbon material into three fractions by using a combination of propane and pentane deasphalting techniques. That process includes (i) mixing the heavy hydrocarbon material with pentane at elevated temperatures and pressures to produce a light fraction containing resins and oils, (ii) mixing the light fraction with propane at high temperatures and pressures to produce a second light fraction comprising oils and a second heavy fraction comprising resins and (iii) recycling at least a portion of the resins fraction back to the pentane deasphalting process. Alternatively, that process may be carried out by subjecting the heavy hydrocarbon material first to a propane deasphalting process to prouce a heavy fraction containing asphaltenes and resins, followed by a pentane deasphalting process on the asphaltene-resin fraction previously obtained to produce a second light fraction comprising resins and a second heavy fraction comprising asphaltenes and recycling at least a portion of the resins fraction back to the propane deashalting process.
U.S. Pat. No. 3,830,732 discloses a two solvent extraction process for producing three fractions from a hydrocarbon charge stock containing asphaltenes, resins and oils. The charge stock is admixed with a first solvent in a volumetric ratio of solvent to charge stock of less than about 4:1 to form a mixture that is introduced into a first extraction zone maintained at an elevated temperature and pressure. The mixture separates within the first extraction zone to produce a first solvent-rich liquid phase containing oils which are free of asphaltenes and resins and a first solvent-lean liquid phase containing asphaltenes and resins. The solvent-lean liquid phase then is contacted with a second solvent containing at least one more carbon atom per molecule than said first solvent and introduced into a second extraction zone. The second extraction zone is maintained at a lower temperature and pressure than the first extraction zone to separate the solvent-lean liquid phase into a second solvent-rich liquid phase containing resins and a second solvent-lean liquid phase containing asphaltenes.
U.S. Pat. No. 4,101,415 discloses a single solvent extraction process for separating a heavy hydrocarbon material into three different fractions by a process employing a two stage solvent treatment wherein different solvent to feed ratios and different temperatures are used in each stage. The charge stock is admixed with the solvent in a volumetric ratio of solvent to feed in the range of 2:1 to 10:1 and introduced into a first extraction zone maintained under temperature and pressure conditions sufficient to cause the mixture to separate into a first solvent-rich fraction containing oils and a first solvent-lean fraction containing asphaltenes and resins. The solvent-lean fraction then is contacted with an additional portion of the solvent and introduced into a second extraction zone maintained at a temperature and pressure lower than in the first extraction zone to cause asphaltic solids to form. The soluble material then is separated from the asphaltic solids.
U.S. Pat. No. 3,774,292 discloses a similar process employing a two stage solvent extraction. In such patent, the solvent-rich fraction which contains resins and oils is admixed with additional solvent and introduced into a second extraction zone maintained at a temperature higher than in the first extraction zone. The solvent-rich phase is separated into a second solvent-rich phase comprising oils and a second solvent-lean fraction comprising resins.
U.S. Pat. Nos. 2,783,188; 2,980,602; 3,003,945; 3,003,946; 3,003,947; 3,005,769; 3,053,751; 3,775,293; and 3,972,807 also disclose processes for the solvent extraction of heavy hydrocarbon materials containing asphaltenes.
It would be desirable to provide a process which can provide the benefits disclosed by U.S. Pat. No. 2,940,920 while employing only a single solvent but without the reduction in product quality caused by the presence of the concurrently separated resinous bodies.